Method for production of maleinamic acid, esters thereof, and maleinimide

Abstract

In the production of an N-unsubstituted maleinimide by the ring-closing alcohol-removing treatment of an N-unsubstituted maleinamic ester for conversion into an imide, an acid catalyst or a mono(cyclo)alkyl sulfuric ester is used for the reaction. In this case, the alcohol concentration in the reaction solution is preferable to be adjusted to a low level. By using a maleinamic acid and an alcohol in conjunction with an inert solvent and an acid catalyst, a mixture of maleinamic acid with an acid catalyst, or a mono(cyclo)alkyl sulfuric ester, a corresponding maleinamic ester is obtained. In a method for the production of a maleinamic acid by the reaction of maleic anhydride with ammonia in an inert solvent, the maleinamic acid is obtained by placing a solution of the maleic anhydride in the inorganic solvent in a reactor, meanwhile introducing ammonia gas into the empty space part of the reactor, and allowing the ammonia gas to be absorbed in the solution through the surface of contact between the solution and the ammonia gas. Further, in the method for the production of a maleinamic acid by the reaction of maleic anhydride with ammonia in an inert solvent, the reaction is carried out while the concentration of the maleic anhydride in the reaction solution is kept at a level of not more than 10% by weight or the ammonia concentration in the reaction solution is kept at a level of not less than 0.001% by weight.

We claim: 
     
       1. A method for the production of a maleinimide, characterized in that the production is attained by heating a maleinamic ester compound represented by the general formula (1): ##STR7## wherein R 1  is an alkyl group of 1 to 8 carbon atoms or a cycloalkyl group of 3 to 8 carbon atoms, in an inert organic solvent in conjunction with a mono(cyclo) alkyl sulfuric acid represented by the general formula (2): ##STR8## wherein R 2  is an alkyl group of 1 to 8 carbon atoms or a cycloalkyl group of 3 to 8 carbon atoms, at a temperature in the range of 20° to 200° C., thereby effecting a ring-closing alcohol-removing reaction. 
     
     
       2. A method as claimed in claim 1, wherein the concentration of alcohol in the reaction system is kept at a level of not more than 3% by weight. 
     
     
       3. A method as claimed in claim 1, wherein the amount of the mono(cyclo)alkyl sulfuric acid to be used is in the range of 0.01 to 2 moles per mole of the maleinamic ester. 
     
     
       4. A method as claimed in claim 1, wherein R 1  and R 2  are identical with each other. 
     
     
       5. A method as claimed in claim 2, wherein the amount of the mono(cyclo)alkyl sulfuric acid to be used is in the range of 0.01 to 2 moles per mole of the maleinamic ester. 
     
     
       6. A method for the production of a maleinimide, characterized in that the production is attained by heating a maleinamic ester compound represented by the general formula (1): ##STR9## wherein R 1  is an alkyl group of 1 to 8 carbon atoms or a cycloalkyl group of 3 to 8 carbon atoms, in an inert organic solvent in conjunction with an acid catalyst at a temperature in the range of 20° to 200° C., thereby effecting a ring-closing alcohol-removing reaction. 
     
     
       7. A method as claimed in claim 6, wherein the concentration of alcohol in the reaction system is kept at a level of not more than 3% by weight. 
     
     
       8. A method as claimed in claim 6, wherein the amount of the acid catalyst to be used is in the range of 0.01 to 2 moles per mole of the maleinamic ester. 
     
     
       9. A method as claimed in claim 6, wherein the acid catalyst has deposited on a solid carrier at least one member selected from the group consisting of sulfuric acid, sulfuric anhydride, sulfonic acid, phosphoric acid, phosphorous acid, and hypophosphorous acid. 
     
     
       10. A method as claimed in claim 6, wherein the acid catalyst is at least one member selected from the group consisting of phosphoric acid, phosphorous acid, and hypophosphorous acid. 
     
     
       11. A method as claimed in claim 7, wherein the amount of the acid catalyst to be used is in the range of 0.01 to 2 moles per mole of the maleinamic ester.